The invention relates to an operating mechanism of a miniature electrical circuit breaker with a molded case housing a pair of stationary and movable contacts, said movable contact being supported by a contact arm actuated by the mechanism between a closed position and an open position, the mechanism comprising :
a manual operating handle coupled to a transmission rod to form a toggle, PA0 a support lever of the contact arm articulated on a pivot of a rotating plate, a relative pivoting movement of small amplitude being allowed between the plate and the support lever due to the presence of a contact pressure spring, PA0 a breakable mechanical link arranged between the plate and the transmission rod, PA0 a trip lever articulated on the plate and being controlled by the trip device to cause breaking of said mechanical link in the event of a fault occurring, resulting in automatic tripping of the mechanism, independently from the handle. PA0 one direct by the latch having a mark coming opposite an indicator of the case, PA0 the other by the handle which is blocked positively by the rod in a stable intermediate position located between the closed and open positions, when the latch is locked by the hangup point after tripping, non-automatic resetting of the mechanism being performed by moving the handle manually from the intermediate position to the open position leading on the one hand to the mechanical link between the handle and the plate being re-established, and on the other hand to the fault indication being cleared.
A device of this kind is known from the document EP No. 244,396, wherein the breakable mechanical link is constituted by a notch of the plate designed to cooperate directly with the cylindrical end of the transmission rod in the set position of the mechanism. A mechanism of this kind is perfectly suited to circuit breakers with low ratings, but for higher ratings the tripping force required to break the mechanical link would be too great, and would lead to oversizing of the trip device, which is impossible because of the small dimensions of the case. According to the documents EP-A-No. 144,691, DE-A-No. 1,904,731 and DE-U-No. 7500060, an intermediate latch and the trip lever of the mechanism are articulated directly on the contact arm. Such an assembly requires great precision of the mechanism components to achieve a good contact pressure.
The object of the invention consists in making a miniature circuit breaker mechanism with a reduced tripping force and good contact pressure simpler to achieve.